Piecing Together the Seismogenic Zone Puzzle of Nicoya, Costa Rica: Insights from the Seismic Cycle Abstract

abstract

  • In this work we present geodetic inversions of GPS data for interseismic, coseismic and postseismic activity in order to illuminate locking, slip, and afterslip along the subduction megathrust beneath Nicoya, Costa Rica. This includes: the coseismic pattern of the Mw 7.6 2012 Nicoya Earthquake as detected from 21 continuous and 18 campaign GPS stations; the initial postseismic response; and 15 years of the preceding interseismic period from campaign and continuous GPS measurements. The coseismic GPS slip vectors revealed large horizontal displacement of ~70cm in the SW direction and uplift of ~53cm in accordance with the Centroid moment Tensor indicating a major thrust event. The coseismic pattern of the data show an inland transition between uplift and subsidence not usually observed in offshore megathrust events, e.g. the M9 2011 Tohoku Earthquake. Furthermore, the horizontal vectors also revealed interesting features such the rotation of GPS vectors, pointing first inwards and then outwards (fan shape), as we move away from the pivot line and toward the coastline. The postseismic GPS vectors show that the direction of displacement in the Peninsula during the first 40 days is the same as the coseismic phase with 5-7cm of horizontal movement and ~3cm of uplift. The 3D Finite Element subduction fault model used for the geodetic inversions is generated using data from numerous existing seismic catalogs with ~36,000 events and regional physiography in an effort to create a realistic interface geometry, and accurately estimate the slip models from surface displacements. The new interface reveals an irregular slab geometry, and the structural variations (e.g. change in dip angle) observed beneath Nicoya appears to be coincident with the transition from East Pacific Rise (EPR) to Cocos Nazca Spreading center (CNS) crust. The GPS observations associated with the Mw 7.6 2012 Nicoya event represent new pieces on the puzzle of the Nicoya seismic cycle and a great opportunity to investigate the role of realistic interface geometries in subduction environment.

publication date

  • 2014

presented at event